1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for use in oil and gas wellbores. More particularly, the invention relates to methods and apparatus for utilizing deployment valves in wellbores.
2. Description of the Related Art
Forming an oil/gas well begins by drilling a borehole in the earth to some predetermined depth adjacent a hydrocarbon bearing formation. After the borehole is drilled to a certain depth, steel tubing or casing inserted in the borehole forms a wellbore having an annular area between the tubing and the earth that is filled with cement. The tubing strengthens the borehole while the cement helps to isolate areas of the wellbore during hydrocarbon production.
A well drilled in a “overbalanced” condition with the wellbore filled with fluid or mud thereby precludes the inflow of hydrocarbons until the well is completed and provides a safe way to operate since the overbalanced condition prevents blow outs and keeps the well controlled. Disadvantages of operating in the overbalanced condition include expense of the mud and damage to formations if the column of mud leaks off into the formations. Therefore, employing underbalanced or near underbalanced drilling may avoid problems of overbalanced drilling and encourage the inflow of hydrocarbons into the wellbore. In underbalanced drilling, any wellbore fluid such as nitrogen gas is at a pressure lower than the natural pressure of formation fluids. Since underbalanced well conditions can cause a blow out, underbalanced wells must be drilled through some type of pressure device such as a rotating drilling head at the surface of the well. The drilling head permits a tubular drill string to be rotated and lowered therethrough while retaining a pressure seal around the drill string.
A downhole deployment valve (DDV) located as part of the casing string and operated through a control line enables temporarily isolating a formation pressure below the DDV such that a tool string may be quickly and safely tripped into a portion of the wellbore above the DDV that is temporarily relieved to atmospheric pressure. An example of a DDV is described in U.S. Pat. No. 6,209,663, which is incorporated by reference herein in its entirety. Thus, the DDV allows the tool string to be tripped into and out of the wellbore at a faster rate than snubbing the tool string in under pressure. Since the pressure above the DDV is relieved, the tool string can trip into the wellbore without wellbore pressure acting to push the tool string out. Further, the DDV permits insertion of a tool string into the wellbore that cannot otherwise be inserted due to the shape, diameter and/or length of the tool string. However, prior designs for the DDV can suffer from any of various disadvantages such as sealing problems at a valve seat, sticking open of a valve member, inadequate force maintaining the valve member closed, high manufacturing costs, long non-modular arrangements, difficulties associated with coupling of control lines to the DDV, and housings with low pressure ratings
Therefore, there exists a need for an improved DDV assembly and associated methods.